Many tents handed out to victims are not designed for winter, while complacency about the aid given so far was a bigger enemy than the weather and the rugged terrain, UN emergency coordinator Jan Vandemoortele said.

"The situation remains very difficult and indeed we are on a knife's edge," Vandemoortele told a news conference in Islamabad, the Pakistani capital.

The October 8 earthquake killed more than 73,000 people in Pakistan and 1,300 in India, but the focus now is on the 3.5 million underfed people facing winter without homes.

The three biggest needs were providing heating for freezing families; corrugated iron sheets so quake victims can build shelters from the rubble of their homes; and winterised tents, Vandemoortele said.

There were encouraging aspects to the aid effort but massive problems remained, adding: "We have got two versions of the story, of the glass being half full and half empty."

Darren Boisvert of the International Organisation for Migration, which is leading efforts to provide shelter, warned that 90 percent of the 420,000 tents handed out "are not winterised".

But Vandemoortele stressed that most people were using blankets and plastic sheeting to bring their tents up to standard to get through the winter.